Automatic conveyor pickup and delivery system



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United States Patent O AUTOMATIC CONVEYOR PICKUP AND DELIVERY 4SYSTEM Alfred l). Benson, Farmington Township, and Edward Mullen, Detroit, Mich.

Application January 9, 1956, Serial No. 557,958

51 Claims. (Cl. 212-126) This invention relates to a conveyor system and more particularly to a system wherein individual identified loads continually `deposited at a plurality of pickup points may be automatically picked up, moved to another floor, selectively carried to either of two delivery points, automatically unloaded and moved to a position permitting other loads to be delivered. This invention also relates to a modified system of the general type indicated above wherein the loads picked up on one door may be selectively delivered to any of a larger number of possible destinations on several oors including the pickup floor.

The present application is a continuation of our prior application Serial No. 686,286, filed on July 26, 1946, for Automatic Conveyor Pickup and Delivery System which is expressly abandoned by the filing hereof.

Industrial material handling systems which have been developed to effect the transportation of individual loads from one work area of a plant to another are generally characterized by the necessity for manual or manually controlled loading and unloading operations. Such necessity frequently presents very serious limitations, especially where the loads are heavy or cumbersome. The advantages incident to a conveyor system of the type indicated above have ledto a great number of attempts to provide conveyors which automatically pick up and deliver loads. However, the numerous difficulties which are encountered in combining automatic pickup with selective delivery have, to the best of our knowledge, heretofore prevented the development of a commercially satisfactory automatic pickup and delivery conveyor system of this type.

In general, the means used in the first-mentioned embodiment of this invention (wherein pickup and delivery points are located on two different floors and selection is limited to two delivery points) include individual selfpropelled conveyor units; an overhead conveyor track passing over each of the pickup points; an overhead conveyor track passing over each of the delivery points; an elevator joining the exit of the pickup track with the entrance to the delivery track; an independent elevator joining the exit of the delivery track with the entrance to the pickup track; a pickup or hoist mechanism on each conveyor unit capable of lowering to engage a load and of raising to an over-passing position; a separate conveyor to move delivered loads away from the delivery point; a three phase system supplied continuously along each conveyor track as well as in the elevators by two power conductor bars with a grounded third phase; two additional conductor bars for purposes of control and actuation of the hoist mechanism; collector shoes carried by the conveyor units for contacting the power, control and boist bars; and a control system for causing each of a number of conveyor units to 1. Continuously circulate around both conveyor tracks; 2. Receive an identifying load signal upon approaching a load;

3. Lower its pickup forks;

2,761,570 Patented Sept. 4, 1956 Pice 4. Hold such forks in lowered position While engaging the load;

5. Raise such forks with the load to an over-passing position;

6. Pass over other loads in its path without lowering its forks;

7. Enter an elevator and stop;

8. Move to the delivery floor;

9. Move in reverse direction out of the elevator and onto the delivery track;

10. Proceed in reverse direction to the proper delivery point;

11. Stop and lower the load to unloading position;

12. Proceed in the reverse direction with forks in lowered positions until free of the load;

13. Raise its forks and proceed to the second elevator;

14. Enter such elevator and stop;

15. Move to the pickup floor;

16. Move in a forward direction out of the elevator and onto the pickup track;

17. Continue in circulation until another load is appreached.

Such control system includes further controls for causing:

1. A load deposited at a pickup point to be identified with respect to its delivery point in a manner which will permit any conveyor unit that may pick up the load to receive a corresponding identifying signal;

2. A conveyor unit, whether traveling in forward or reverse direction, to stop upon approaching another unit;

3. A conveyor unit to stop upon contacting any other obstacle;

. Each elevator to return to its normal receiving position after a conveyor unit has passed out of it;

. A conveyor unit to wait for an elevators return if it is not in receiving position;

. Movement by separate conveyor means of delivered loads to a position permitting following conveyor units to unload;

7. The approach of a conveyor unit to be stopped while a preceding unit is delivering its load.

in connection with this first embodiment, alternative elevator means are provided to move conveyor units between floors wherein a pair of counterbalanced elevators join the exit of the pickup track with the entrance to the delivery track and an independent pair of counterbalanced elevators join the eXit to the delivery track with the entrance to the pickup track, branch tracks being provided leading to and from each of the counterbalanced elevators as well as an alternating track switch for leading an entering conveyor unit to whichever elevator is in receiving position.

ln adapting this conveyor system to single iioor operation wherein loads are picked up and delivered on the saine floor, it would be possible to simulate the means used in the two floor operation by merely substituting a track switch for each elevator. In such case a conveyor unit would pass from the pickup track through a track switch, stop, wait for the switch to move to its delivery track position, move in reverse direction back through the track switch, etc. However, it has been found more desirable to avoid the use of such track switches in single oor operation by providing a continuous endless conveyor track with means for causing the conveyor unit to reverse its direction only yduring unloading operations. The control system for this latter method causes each conveyor unit to load signal upon approaching a load;

3. Lower its pickup forks;

4. Hold such forks in lowered position while engaging the load;

5. Raise such forks with the load to an over-passing position;

6. Pass over other loads in its path without lowering its forks;

7. Proceed in forward direction slightly past the proper delivery point;

8. Reverse in direction of travel;

9. Stop and lower the load to unloading position;

10. Move in reverse direction with forks in lowered direction until free of the load;

11. Raise its forks;

ll2. Stop and proceed in a forward direction over-passing the delivered load; 13. Continue in circulation until another load is approached.

Further controls similar to those described for two oor operation are also provided for causing 1. A load deposited at a pickup point to be identified as to delivery point;

2. A conveyor unit to stop upon approaching another unit;

3. A conveyor unit to stop upon contacting any other obstacle;

4. Movement, by separate conveyor means, of delivered loads to a position permitting following conveyor units to unload;

5. The approach of a conveyor unit to be stopped while a preceding unit is delivering its load.

Where it is desired to adapt the present pickup and delivery system to more than two delivery points, an alternative means for identifying loads and selecting delivery points is provided. Such alternative selective means utilizes an add and subtract stepping relay located on each conveyor unit capable of stepping in one direction in response to a series of electrical impulses and in the other direction in response to a different series of electrical irnpulses. A load to be picked up and delivered to a particular delivery point is identified when placed on a pickup rack by energizing a corresponding number of impulse sections in the hoist conductor bar which actuate the stepping relay of a conveyor unit while it is picking up the load. As the conveyor unit then passes each delivery point, an impulse section causes the stepping relay to take one step back and when the relay has stepped back to a zero position, the conveyor unit automatically stops and unloads.

In order to incorporate selectivity as to delivery floor, a similar stepping relay is utilized which is actuated during the pickup operation by a separate group of impulse sections and is stepped back to zero by a group of impulse sections located at the entrance to the elevator whereupon a signal is established for causing the elevator to move to a corresponding floor. A branch track by-passing the elevators is provided in order to incorporate deliveries on the pickup floor as well as other tloors and also to permit unloaded conveyor units to circulate on the pickup oor without moving to other oors.

In accordance with the above general description, it is the principal object of the present invention to provide a conveyor system wherein individual identified loads continually deposited at a plurality of pickup points may be automatically picked up, moved to another floor, selectively carried to either of two delivery points, automati* cally unloaded and moved to a position permitting other loads to be delivered.

Another object is to provide a modiiied conveyor system wherein delivery points are located on the same oor as the pickup points.

A further object of the invention is to provide a modied conveyor system wherein identified loads may be delivered to a larger number of possible destinations on several floors including the pickup oor.

Another object is to provide individual self-propelled conveyor units with a pickup mechanism capable of being lowered to a pickup position and raised to an over-passing position.

A further object is to provide automatic elevator means for joining pickup and delivery conveyor tracks.

Another object is to provide supplementary conveyor means for automatically moving loads after their delivery to a non-blocking position.

A further object is to provide a power supply system adaptable to meet the requirements of the present invention.

Another object is to provide a control system for accomplishing each of the steps indicated above.

These and further objects will appear more clearly from the following detailed description of the particular embodiments of the present invention and by reference to the drawings forming a part hereof and wherein,

Fig. 1 is a schematic plan view of a conveyor layout on two floors with elevators joining the tracks on each floor in accordance with the first embodiment of the present invention.

Fig. 2 is a schematic plan view of a modified conveyor layout for single floor pickup and delivery operation.

Fig. 3 is a schematic plan view of a modified multiple floor conveyor layout with elevators joining the tracks on each oor and with multiple delivery points located on each floor including the pickup oor.

Fig. 4 is a side elevation of a conveyor unit shown in assembled position on the conveyor track including the pickup mechanism mounted thereon.

Fig. 5 is a plan View of the conveyor unit shown in Fig. 4 omitting the conveyor track and certain of the trolleys.

Fig. 6 is an end elevation of the conveyor unit shown in Fig. 4.

Fig. 6a is an enlarged end View of the conveyor track and conductor bars shown in Fig. 6.

Fig. 7 is a fragmentary view taken along the line 7-7 of Fig. 4.

Fig. 8 is a fragmentary view taken along the line 8-8 of Fig. 4.

Fig. 9 is a fragmentary view taken along the line 9-9 of Fig. 6.

Fig. l() is a fragmentary view taken along the line 10-10 of Fig. 4.

Fig. l1 is a schematic diagram of the control circuit located in each self-propelled conveyor unit.

Fig. l2 is a schematic plan view of a loading rack used at the various pickup points.

Fig. 13 is an end elevation of the rack shown in Fig. 12.

Fig. 14 is a schematic diagram of the control circuit at each pickup point.

Fig. 15 is an enlarged schematic view of the elevators shown in Fig. 1.

Fig. 16 is a schematic diagram of the control circuit for each of the elevators.

Fig. 17 is an enlarged schematic view of the automatic delivery point shown in Fig. 1 including the belt conveyor used at such delivery point.

Fig. 17a is a fragmentary side elevation of the belt conveyor taken along the line a-a of Fig. 17.

Fig. 18 is a schematic diagram of the control circuit for such automatic delivery point.

Fig. 19 is an enlarged schematic view of the semi-automatic delivery point shown in Fig. 1.

Fig. 20 is a schematic diagram of the control circuit for such semi-automatic delivery point.

Fig. 21 is a schematic view of an alternative elevator system used in two oor operation showing a pair of counterbalanced elevators operating between pickup and delivery floors and a second pair of counterbalanced ele- Vators operating between delivery and pickup floors as 45 well as track switches used in connection with each pair of elevators.

Fig. 22 is a schematic diagram of the control circuit for such alternative elevator system.

Fig. 23 is a schematic view of the conductor bars at the first delivery point used in single floor operation.

Fig. 24 is a schematic diagram of the control circuit located at such delivery point.

Fig. 25 is a schematic view of the conductor bars at the second delivery point used in single floor operation.

Fig. 26 is a schematic diagram of the control circuit locatedl at such second delivery point.

Fig. 27 is a schematic plan view of a typical pickup point used in the multiple floor-multiple delivery point system.

Fig. 28 is a schematic diagram of the control circuit located at each pickup point in the latter system.

Fig. 29 is a perspective view of the add and subtract stepping relay used in connection with multiple floor and multiple delivery point selection.

Fig. 30 is a schematic diagram of the modified control system for a conveyor unit incorporating the use of add and subtract stepping relays.

Fig. 3l is a schematic plan View of the elevator used in the multiple floor system for moving conveyor units from the pickup floor to a delivery iloor including conveyor lines leading to and from and by-passing such elevator and including a typical delivery point on the pickup iioor and a typical delivery point on one of the delivery floors.

Fig. 32 is a schematic diagram of the control circuit for a typical delivery point on the pickup floor as well as a typical delivery point on one of the delivery oors.

Fig. 33 is a schematic diagram of the control circuit for the elevator shown in Fig. 3l.

Fig. 34 is a schematic plan view of the return elevator used in the multiple floor system including conveyor lines leading to and from and by-passing such elevator.

Fig. 35 is a schematic diagram of the control circuit for the return elevator shown in Fig. 34.

CGNVEYOR TRACK AND ELEVATOR LAYOUT Referring to Fig. l showing a layout of the conveyor track in accordance with the lirst embodiment of the present invention, it will be seen that a single track 55 passes over cach of the pickup points 56a, 56h, etc, and that the exit 57 of the pickup track leads to an elevator 58 which is provided with a section of track 59 suspended from the top of the elevator which may be brought into alignment with the exit e7 of the pickup track 55. Movement of the elevator 5b to the delivery floor brings the section of the track 59 within the elevator into alignment with the entrance @il to the delivery track 61. It will be noted that the entrance 6i) to the delivery track joins the elevator 58 on the same side as the eXit 57 of the pickup track so that a conveyor unit entering the elevator 58 in a forward direction will leave such elevator in a reverse direction as it enters the delivery track 6l.

The delivery track 61 passes over two delivery points 62a and 62h. The delivery point 62a has been chosen to illustrate an automatic unloading operation incorporated in the present conveyor system and includes an automatic belt conveyor 63 for moving delivered loads to the side of the conveyor track as fast as they may be delivered in order to make way for each subsequent load. The delivery point 6211, which might if desired also incorporate the automatic unloading features, has been chosen in this case to illustrate an alternative method of delivery wherein the conveyor unit will stop and lower the load awaiting manual or manually controlled removal of the load and restarting of the conveyor unit. Thus, for this delivery point, no automatic conveyor such as the belt conveyor 63 is used. The exit 64 of the delivery conveyor track 61 leads into a second elevator 65 similar in operation to elevator 58 which, upon movement to the pickup floor, joins the entrance 66 to the pickup track 55.

The conveyor layouts shown in Figs. 2 and 3 illus- 6 trate the modified conveyor systems incorporating single floor pickup and delivery and multiple floor-multiple delivery point operations, respectively, and will be more fully explained in connection with such modified systems.

SELF-PROPELLED CONVEYOR UNIT Referring to Figs. 4 to 9 inclusive, it will be seen that the conveyor unit comprises generally a traction wheel and driving motor assembly designated as A, a supporting framework B for mounting a hoist motor and reduction gearing therefor, a forwardly extending xed framework C and a movable pickup mechanism D.

The driving wheel 10 is rotatably journaled in the framework 11 and held in compression against the lower surface 12 of the conveyor track 13 by the vertical spacing effected by the trolley brackets 14 between trolley wheels 1S journaled thereto to roll upon the upper surface 16 of the conveyor track 13 and the framework 1l suspended from the trolley brackets 14. A three phase motor 17 mounted on the framework 11 and suitably geared to the driving wheel 10 by means not shown rotates the driving wheel 10 in either a forward or reverse direction in a manner hereinafter described more fully.

The driving assembly A through a drawbar 18 imparts motion to the rear trolley assembly 19 suspended from the conveyor track by the trolley wheels 2t) and trolley brackets 21. The framework B is suspended from the trolley assembly 19 by a bolt 22 and mounts a hoist lmotor 23, reduction gearing 24, a cable drum 25 and a cable pulley 26, as most clearly shown in Figs. 7 and 8.

Bracket members 27 attached to the lower end of the framework B serve to pivotally attach extension arms 2S of the pickup mechanism D which are in turn pivotally attached at their outer ends 29 to a pickup fork 30 which, in the present embodiment, serves to engage and support the load to be conveyed. A cable 31 atttached to the cable drum 25 passes around the cable pulley 26 and a second pulley 32 suitably journaled at the upper end of the supporting framework C. From the cable pulley 32 the cable 3l passes around a sheave 33 and is securely attached, as shown at 34, to the outer end 35 of the upper extension arm 28.

It will thus be seen that when the hoist motor 23 is run in a direction such as to unwind the cable 31, the weight of the pickup mechanism D will cause it to be lowered to its pickup position, as shown in phantom outline, and that when thc hoist motor 23 is run in the opposite direction winding the cable 31 on the drum 2.5, the pickup mechanism will be raised to its upper position. lt will be noted that the parallel construction of the extension arms 2S will cause the fork 30 to remain in a horizontal position at all times.

The position of the pulley 32 on the supporting member C, which is in turn supported at its forward end by the trolley assembly 36 through bracket members 37 and trolley wheels 38 causes the weight of the load supported by the fork 3b to be distributed between the forward trolley assembly 36 and rear trolley assembly 19.

A forward bumper arm 39 is pivotally connected to a bracket 4t? which is in turn mounted on the forward trolley assembly 36 and is positioned to contact the fanshaped rearward bumper member 41 of an adjacent conveyor unit on approaching such unit from the rear. Such contact raising the forward bumper arm serves to depress a forward bumper limit switch FBLS opening an electrical contact which, when the conveyor unit is travcling in a forward direction, stops the driving motor 17 thereby stopping the conveyor unit. At the same time the rear bumper 41 which is pivotally attached at 43 to the rearward trolley assembly 19 moves downward depressing a rear limit switch RBLS thereby opening another electrical contact. As will be hereinafter more clearly described, these contacts are so arranged in the conveyor unit control circuit so as to cause only the driving motor of the overtaking conveyor unit to be stopped, whether such overtaking conveyor unit is traveling in a forward or reverse direction.

A solenoid brake adapted to quickly stop the driving motor upon any interruption in its energizing circuit operates to stop the conveyor unit in a relatively short space so as to prevent any damage to either conveyor unit in the event that one overtakes the other. In this connection, the forward bumper arm 39 upon contacting the rearward bumper 41 is free to ride up the inclined surface 50 and to thereupon slide over such bumper in a manner which permits the approaching conveyor unit to move a substantial distance toward the other conveyor unit after the initial depression of the respective limit switches, such distance exceeding the required stopping distance for a conveyor unit traveling at full speed.

A lower bumper ring 4S is suspended from the framework B by bolts 46 and 47 in a manner whereby contact with an obstacle in the path of the conveyor unit from any side will move the ring 45 laterally and upwards causing a cup-shaped member 48 centrally attached within the ring 45 to depress a lower bumper limit switch LBLS and thereby stop the driving motor 17.

As shown in Figs. 8 and 9, a hoist limit switch HLS and a lower limit switch LLS mounted on the framework B are actuated respectively by the movement of the hoist mechanism D to its upper and lower positions through the contact of dogs 27a, 2712 mounted on plate 27e to rotate with the hub of extension members 28.

POWER SUPPLY As shown in Figs. 4, 6 and l0, power conductor bars PBI, PBZ mounted in insulator blocks 50 are contacted by power collector shoes P1, P2 which are suitably mounted on the conveyor bracket as shown at 54 and urged by spring means to contact such conductor bars. A control conductor bar CB1 and a hoist conductor bar HB1 are also contacted respectively by a control shoe C1 and hoist shoe H1. The additional hoist shoes H2 and H3, which are used only in connection with the modified multiple floor-multiple delivery point system, likewise contact the hoist conductor bar HB1.

A three phase power supply is carried continuously along the conveyor track 13 by the power conductor bars PBl and PB2, the third phase being grounded through the main body of the conveyor track. Power phases L1 and L2 are carried by the conductor bars PE1 and PBZ respectively on the pickup floor, as well as in the elevator 58 during its movement to the delivery floor. Reverse phases L2 and L1 are carried by the corresponding conductor bars PB1, FB2 on the delivery iloor at all times and in the elevator 58 as soon as it reaches delivery tloor level. The control conductor bar CB1 is normally energized thrugh direct connection to the power bar PBl on the pickup floor and PB2 on the delivery oor so that it is supplied with power phase L1 on both floors. Such conductor bar is provided with insulated control sections to be hereinafter more fully described. The conductor bar H1 is not directly energized by either of the power bars but is used in completing certain signal circuits to actuate the hoist mechanism of the selfpropelled conveyor unit in a manner hereinafter described.

CONTROL SYSTEM 'I'he control system used in the first embodiment of the present conveyor system may be divided into several parts including those respectively located in the selpropelled conveyor unit, at each pickup point, at each elevator, and at the delivery points. The control circuits located at these various points are primarily directed to control the operation of the various motors which are provided to drive the conveyor units, to operate the hoist mechanism on each conveyor unit, to operate each elevator, and to operate the belt conveyor located at the automatic delivery point. The components of the various control circuits include standard commercially available latching relays which are closed and tripped by separate circuits and are provided with both normally open and normally closed contacts reversed upon the closing of the relays; spring return relays having contacts reversed when the relay is energized and returned to normal position upon the opening of the energizing circuit; magnetic line contactors which operate when energized to close circuits from the power supply to the various motors; reversing line contactors for the elevator motors permitting them to be run in a forward or reverse direction by reversing the phase connections; limit switches which operate through physical contact to open normally closed and close normally open contacts; timers which are electrically energized and serve to reverse normal contacts for a predetermined period of time and then return such contacts to their normal position; and push button stations provided for manual control. These control circuits also include certain insulated sections in the control and hoist conductor bars CB1 and HB1 which are energized and de-energized for control purposes; pulse sections in the control conductor bar CB1 which are momentarily energized when contacted by the pickup shoe of a conveyor unit; and iron core reactors having an impedance sufiiciently high to prevent a short circuit white permitting passage of sufficient current to energize a control relay. As previously indicated, each conveyor unit is provided with pickup shoes P1, P2, C1, and H1 for continuously contacting the power conductor bars PBI and FB2, the control conductor bar CB1 and the hoist conductor bar HB1 (see Fig. 4).

a. Conveyor unit Referring to Fig. ll which shows a schematic diagram of that portion of the control circuit located within each conveyor unit, the vertical line designated as L3 represents the grounded third phase of the power supply and the other vertical lines represents the power phases carried by the conductor bars FB2 and PBI.. Connections to the latter two lines represent electrical contacts made directly through the power pickup shoes P2 and P1. Arrows designated as L1 all floors indicate electrical contacts established through the pickup shoe C1 contacting the control conductor bar CB1. The divided dotted arrows designated L2 and L1 at the bottom of the diagram indicate contacts made by the pickup shoe H1 with insulated sections of the hoist conductor bar HB1 at pickup and delivery points.

All control circuits in the conveyor unit itself are directed to control the operation of the conveyor unit motor and the hoist motor. These three phase motors are each supplied with power directly from the power pickup shoes P1 and P2.

The starting and stopping of the conveyor unit motor is controlled by the contacts M of a magnetic line contactor which are closed when the coil encircled M of such contacter is energized. Directional control of the conveyor unit motor is accomplished solely through the phase relationship of the power carried in conductor bars PBI and PB2. The conveyor unit motor which is normally driving the conveyor unit is stopped whenever the control shoe C1 contacts a de-energized section in the conductor bar CB1, the lower bumper limit switch is depressed, the forward or rear bumper limit switch FBLS or RBLS is depressed, depending on the direction of travel, or the stop push button of the push button station PBS is depressed.

The operation of the hoist motor in one direction or the other is controlled by the contacts L(H) and H(L) of a reversing line contacter which are closed respectively when the coil encircled L(H) or H(L) is energized. During automatic operation, the energizing circuits for either of these coils must pass through one or" two contact's of a spring return relay CR2, the -upper or lower limit switch HLS or LLS, and one of four contacts of a mechanically held relay CRS. The condition of the contacts of these relays is in turn controlled by certain additional control relays including mechanically held relays CR1 and CR4 as well as a spring return relay CRS.

More specifically, the condition of the circuit represented by the schematic diagram, as shown conforms to that of a conveyor unit with its hoist mechanism in raised position before energizing the power conductor bars. Assuming the conveyor unit to be on the pickup iloor, upon energizing the power conductor bars PB1 and FB2, a circuit from L3 to L1 through the contacts of the push button station PBS, which is shown depressed to automatic position, the energizing coil of the magnetic line contactor encircled M, the normally closed contact of the reverse upper limit switch RBLS, the normally closed contact of control relay CRS, and the normally closed contact of the lower bumper limit switch LBLS energizes lthe magnetic line contactor thereupon closing the contacts M and starting the conveyor unit motor in a forward direction. With the M contacts closed, a circuit from L2 to L1 through the energizing coil encircled CRS of control relay CRS is established reversing the normal contacts of such relay and thereupon a circuit from L2 to L1 through the normally opened contact of control relay CRS, the normally closed contact of control relay CRS and the closing coil of control relay CRS energizes such closing coil reversing all CRS contacts. The reversal of the CRS contacts in series with the forward and rear bumper limit switch contacts FBLS and RBLS causes the circuit to the line contactor for the conveyor unit motor to now pass through the forward bumper limit switch FBLS so that a physical contact made by the forward bumper of the conveyor unit will open the circuit to such line starter thereby stopping the conveyor unit, while a contact with the rear bumper opening the normally closed contact RBLS will not interrupt such circuit. It will be noted that a contact with the bumper ring 4S, as shown in Fig. 4, will open the LBLS Contact in this circuit thereby interrupting the power to the conveyor unit motor. The closing of control relay CRS also reverses the CRS contacts in series with the energizing coils of the reversing line contactor encircled L(H) and H(L). The upper energizing coil as shown in the diagram, which controls the contacts L(H) in series with the hoist motor and on the pickup floor, when energized, causes such hoist motor to operate in a direction lowering the hoist mechanism. The lower energizing coil which controls the contacts H(L) when energized, causes the hoist motor to operate in a reverse direction raising the hoist mechanism. This results from the reverse application of two phases to the hoist motor when the H(L) contacts are closed. Thus, with the pickup mechanism in its raised position and with the control relay CRS closed reversing its normal contacts, it is necessary, in order to lower the pickup mechanism, to establish a circuit from L3 to L2 through the normally open contact of control relay CRZ, the normally open contact of the lower limit switch LLS, the normally open contact `of control relay CRS and the energizing coil encircled L(H). Since the normally open CRS contact is now closed, it remains for control relay CRZ to be energized in order to start the hoist motor to lower the hoist mechanism. In point of time, it is desirable for such lowering of the hoist mechanism to take place while the conveyor unit is approaching a load, rel be established through the normally closed contact of contnol relay CRZ, the normally open contact of the upper hoist limit switch HLS (which closes upon the lowering of the hoist), the normally open contact of control relay CRS and the line contactor energizing coil encircled H(L). This time actuation of control relay CR2 is accomplished through a section of the hoist conductor rail HB1 extending from a point somewhat preceding each loading point to a point past such loading point. Such section, which may be energized with either L1 or LZ phase in a manner presently to be described, when contacted by the hoist pickup shoe H1 of the conveyor unit, establishes a circuit from L3 to L2 or L1, as the case may be, through the normally closed contact of control relay CR4, the normally closed contact of control relay CR1, and the energizing coil of control relay CRZ.

Since the control relay CR2 is energized through the initial contact of the conveyor unit pickup shoe H1 with an energized section of the hoist conductor bar HB1, the hoist motor is energized in a lowering direction and continues to lower the pickup mechanism until the lower limit switch LLS contact is opened. When the load has been engaged and the pickup shoe H1 passes off of such energized section of the hoist conductor bar H1, or such section becomes de-energized, control relay CRZ returns to its de-energized position thereupon closing a circuit through the normally closed contact of control relay CRZ, the normally open contact of the upper hoist limit switch HLS, the normally open contact of control relay CRS and the line contactor energizing coil encircled H(L) thereupon starting the hoist motor in a raising direction. When the hoist reaches its upper position, the upper hoist limit switch HLS is depressed thereupon opening the HLS Contact and stopping the hoist motor.

In order to prevent the subsequent lowering of the pickup mechanism upon approaching a second load, it is necessary to prevent a circuit from again energizing control relay CRZ until after the rst load has been delivered. This is accomplished by control relay CR1 which is closed by a circuit from L2 to L1 through a normally open contact lof control relay CRS, a normally open contact of the lower limit switch LLS, a normally closed contact of control relay CR1 and the closing coil of control relay CR1. As soon as the lower limit switch LLS is depressed, upon the lowering of the pickup mechanism to engage a load, closing the normally open contact of such switch in series with the closing coil of control relay CR1, such relay is closed. The reversal of CR1 contacts opens the normally closed contact of such relay in series with the energizing coil of control relay CRZ and, once control relay CRZ has become de-energized after the tirst load has been engaged, the subsequent closing of its energizing circuit upon the conveyor units approach to another load is thereby prevented. However a circuit for maintainingv control relay CRZ in an energized condition as long as the hoist shoe H1 remains in contact with an energized section in the hoist conductor bar is established through the now closed CRZ contact circuit in parallel with that passing through the now open CR1 contact.

Identiiication of the load as between the two delivery points is accomplished by control relay CR4 which is closed when the energized section of the hoist conductor bar at the pickup point is energized with current of L2 phase but remains unclosed when such section is energized with current of the L1 phase. It will be noted that the circuit from LS through the energizing coil of control relay CRZ is effective to close control relay CRZ, regardless of which phase of current is used to energize the hoist conductor bar. The resistance of the energizing coil for control relay CRZ is too high to permit a circuit from L3 to close control relay CR4 so that the only available circuit for closing such relay is from the energized hoist conductor bar. If such conductor bar is energized with the L2 phase, a circuit from such conductor bar through the closing coil of control relay CR4 to L1 is established closing control relay CR4 as soon as the normally open 

